Method and magnetic resonance device to determine a background phase curve

Abstract

In a magnetic resonance (MR) device and method to determine a background phase curve in MR image data, in first MR image data and in second MR image data that respectively represent different segments (for example different slices) of an examination subject, first and second pixels are identified that represent essentially stationary tissue, and the associated phase values are determined. Phase correction values for the first MR image data are determined depending on the phase values determined for the first and second pixels that represent essentially stationary tissue.

We claim as our invention: 
     
       1. A method to determine a background phase curve in magnetic resonance (MR) image data obtained from an examination subject in a phase-sensitive magnetic resonance data acquisition procedure wherein said MR image data are acquired from respective segments of the examination subject, said MR image data representing a plurality of pixels, said method comprising the steps of:
 in a computerized processor, determining, in first MR image data of said MR image data, which represent a first of said segments of said examination subject, at least one first phase value respectively for at least one first pixel that represents substantially stationary tissue in said first MR image data; 
 determining a phase correction value for said first MR image data dependent on said at least one first phase value; 
 in said computerized processor, determining, for second MR image data of said MR image data, which represent a second of said segments of said examination subject different from said first segment, at least one second phase value for at least one second pixel that represents substantially stationary tissue in said second MR image data; and 
 in said computerized processor, determining phase correction values depending on said at least one first phase value and said at least one second phase value. 
 
     
     
       2. A method as claimed in  claim 1  wherein said first segment is a first slice of the examination subject and said second segment is a second slice of the examination subject, said first slice and said second slice being different from each other. 
     
     
       3. A method as claimed in  claim 2  wherein said first slice and said second slice are offset relative to each other in an axial direction of the subject. 
     
     
       4. A method as claimed in  claim 2  wherein said first slice and said second slice are offset relative to each other along a longitudinal direction of a vessel in said subject. 
     
     
       5. A method as claimed in  claim 1  comprising determining said phase correction values using at least one fit function dependent on said at least one first phase value and said at least one second phase value. 
     
     
       6. A method as claimed in  claim 1  comprising determining said phase correction values by determining a first fit function dependent on said at least one first phase value and a second fit function dependent on said at least one second phase value, and determining said phase correction values from said first fit function and said second fit function. 
     
     
       7. A method as claimed in  claim 6  comprising determining said phase correction values by averaging said first fit function and said second fit function. 
     
     
       8. A method as claimed in  claim 1  comprising identifying at least one additional set of said MR image data, which represent at least one additional segment of the subject that differs from said first segment and said second segment and, for said at least one additional set of said MR image data, identifying at least one additional pixel that represents substantially stationary tissue in said at least one additional set of said MR image data, and determining at least one additional phase value associated with said at least one additional pixel, and determining said phase correction values also dependent on said at least one additional phase value. 
     
     
       9. A method as claimed in  claim 1  comprising also determining phase correction values for pixels in at least one of said first MR image data and said second MR image data that do not represent substantially stationary tissue. 
     
     
       10. A method as claimed in  claim 1  comprising, in said computerized processor, implementing a phase correction of said first MR image data and said second MR image data using the determined phase correction values. 
     
     
       11. A method as claimed in  claim 10  comprising determining a flow profile of a flow represented in said first and second MR image data, dependent on at least one of the phase-corrected first MR image data and the phase-corrected second MR image data. 
     
     
       12. A method as claimed in  claim 1  comprising acquiring said first MR image data in a first data acquisition and acquiring said second MR image data in a second data acquisition, with a spacing between a position of the first segment in the first data acquisition and a position of the second segment in the second data acquisition being less than a predetermined threshold. 
     
     
       13. A method as claimed in  claim 12  comprising executing said first data acquisition to obtain said first segment in a region of an isocenter of the magnetic resonance data acquisition device, and executing the second data acquisition to acquire the second segment of the examination subject also in said region of said isocenter of said MR device. 
     
     
       14. A method as claimed in  claim 1  comprising acquiring said first MR image data in a first data acquisition and acquiring said second MR image data in a second data acquisition with the examination subject being moved relative to the MR data acquisition device between the first data acquisition and the second data acquisition. 
     
     
       15. A method as claimed in  claim 14  comprising executing said first data acquisition to obtain said first segment in a region of an isocenter of the magnetic resonance data acquisition device, and executing the second data acquisition to acquire the second segment of the examination subject also in said region of said isocenter of said MR device. 
     
     
       16. A non-transitory computer-readable storage medium encoded with programming instructions, said storage medium being loaded into a computerized control and evaluation system of a magnetic resonance system, and said programming instructions causing said computerized control and evaluation device to:
 in first MR image data of said MR image data, which represent a first of a plurality of segments of said examination subject, determine at least one first phase value respectively for at least one first pixel that represents substantially stationary tissue in said first MR image data; 
 determine a phase correction value for said first MR image data dependent on said at least one first phase value; 
 for second MR image data of said MR image data, which represent a second of said plurality of segments of said examination subject different from said first segment, determine at least one second phase value for at least one second pixel that represents substantially stationary tissue in said second MR image data; and 
 determine phase correction values depending on said at least one first phase value and said at least one second phase value. 
 
     
     
       17. A magnetic resonance (MR) apparatus comprising:
 an MR data acquisition unit configured to execute a phase-sensitive MR data acquisition procedure to acquire MR image data from respective segments, in a plurality of segments, of an examination subject, said MR image data representing a plurality of pixels; 
 a computerized processor configured to determine, in first MR image data of said MR image data, which represent a first of said segments of said examination subject, at least one first phase value respectively for at least one first pixel that represents substantially stationary tissue in said first MR image data; 
 said computerized processor being configured to determine a phase correction value for said first MR image data dependent on said at least one first phase value; 
 said computerized processor being configured to determine, for second MR image data of said MR image data, which represent a second of said segments of said examination subject different from said first segment, at least one second phase value for at least one second pixel that represents substantially stationary tissue in said second MR image data; and 
 said computerized processor being configured to determine phase correction values depending on said at least one first phase value and said at least one second phase value. 
 
     
     
       18. A magnetic resonance apparatus as claimed in  claim 17  wherein said magnetic resonance data acquisition device is configured to acquire said first MR image data to represent a first slice of the subject and to acquire the second MR image data to represent a second slice of the examination subject, said first and second slices being different from each other.